Question

先化简，再求值（x-1)(x-2)-3x(x-4)-2(x+2)(x-1)，其中x=-1/2

Answer 1

（x-1)(x-2)-3x(x-4)-2(x+2)(x-1)
=(x-1)[(x-2)-2(x+2)]-3x(x-4)
=(x-1)(x-2-2x-4)-3x(x-4)
=(x-1)(-x-6)-3x(x-4)
=-x方-5x+6-3x方+12x
=-4x方+7x+6
把x=-1/2代入上式，得
原式=3/2

Answer 2

(x-1)(x-2)-3x(x-4)-2(x+2)(x-1)
=x^2-3x+2-3x^2+12x-2(x^2+x-2)
=x^2-3x+2-3x^2+12x-2x^2-2x+4
=x^2-2x^2-3x^2+12x-3x-2x+2+4
=-4x^2+7x+6
=-4*(-1/2)^2+7*(-1/2)+6
=-1-7/2+6
=-9/2+6
=3/2